The present invention relates to a boride-based refractory material or, more particularly, to a boride-based refractory material having remarkably improved mechanical strengths and hardness at high temperatures as well as high heat resistance based on a metal diboride of the MB.sub.2 type or an equivalent boride such as M.sub.2 B.sub.5 type boride as the base component.
Among various classes of highly refractory materials, metal diboride-based ones belong to one of the most promising classes owing to their high melting points and high hardness as well as sufficiently high mechanical strengths at high temperatures in general so that their application to cutting tools and building materials for internal combustion engines and rockets and the like is now under rapid development. On the contrary to the above mentioned excellent properties of the metal diboride-based refractory materials, they are rather defective of the brittleness and low bending strength, especially, when the refractory material is composed essentially of a metal diboride of the MB.sub.2 type or a metal boride of the M.sub.2 B.sub.5 type which may be crystallographically equivalent to the MB.sub.2 type diboride at elevated temperatures.
Extensive investigations have hitherto been undertaken to develop a metal diboride-based refractory material fully exhibiting the excellent properties inherent to the metal diborides and still free from the above mentioned defects of brittleness or low bending strength of the prior art materials. The investigations have been directed to the improvement of the material by the addition of a suitable binder component to a metal diboride and there have been proposed several kinds of binders which may be an alloy of nickel and phosphorus or a boride of nickel, iron, cobalt, manganese or titanium. There has further been disclosed that a metal boride of the M.sub.2 B.sub.5 type such as W.sub.2 B.sub.5 and Mo.sub.2 B.sub.5, which has the same crystallographic structure at high temperatures as the metal diborides of the MB.sub.2 type, is more advantageous in a sintered refractory material in respect of the mechanical strengths at high temperatures (see, for example, copending U.S. applications Ser. Nos. 89,487, 973,957 and 127,434 now U.S. Pat. Nos. 4,259,119; 4,246,027; and 4,292,081, respectively).
It is of course desirable to obtain a metal diboride-based refractory material having still higher strengths than those obtained in the above described impoved formulations and the inventors have continued their efforts to discover more preferable formulations for a high-strength refractory material on the base of a metal diboride.